The real-life consequences of drug use cannot be determined with laboratory-controlled experimental studies. The complete nature and extent of these consequences may not appear until many years after adolescence into adulthood. We use a unique, rich, and comprehensive database over a 20-year span of our subjects lives with careful and complex analyses to evaluate whether drug use has a reliable impact on changing physical and psychosocial functioning later in life. This project uses a unique and rich 20-year database to conduct comprehensive structural equation model analyses of these data. We develop contrast, elaborate, and refine current theories to explain and predict the long-term psychosocial and health-related consequences of using drugs as a teenager or young adult, and evaluate these theories using latent-variable models. In addition, a few carefully selected multi-wave prospective data bases will also be analyzed in cooperation with their owners to cross- validate and extend our findings.